English: this project documents the detailed process of building a nonlinear model of the Twin Rotor MIMO System (TRMS), a laboratory helicopter by Feedback Instruments Ltd. In the field of control engineering the TRMS is a benchmark prototype used for identification experiments and controller designs. The TRMS is a complex system of two strongly coupled inputs and outputs with nonlinear behavior, which are totally dependent on the initial conditions. Such features make for easy destabilization and turn the dynamic model identification into a considerable challenge. Although numerous researchers have developed diverse models of the TRMS, neither their models nor those provided by the manufacturer fit our laboratory equipment, a fact that shows the need for building our own model. The present thesis begins with an informative explanation of how real helicopters work, in order to contextualize our project and present the most important dynamic aspects dealt with. Then the laboratory prototype is described in detail and the dynamic behavior of the TRMS is modeled rigorously from the first principles of physics, in particular, by applying Newton's laws for rotation. Later, after obtaining the analytical relations describing the motion of the device, the values of some key parameters are estimated and fitted to harmonize the analytical equations to the reality of our TRMS. To carry out this experimental identification, several numerical methods, especially the Levenberg-Marquardt and the pattern search methods, are considered and compared. Finally, the model obtained is judged by applying various validation criteria and its validity is shown by several experimental results.